Heat reflecting fenestration products have become increasingly popular for architectural and vehicular window use. Such products have been found to be highly effective in reducing air conditioning costs and in improving the quality of transmitted visible light.
The most common such fenestration products are composites having multiple thin layers which cooperate with one another to reduce the transmission of infrared and near infrared waves, while allowing the transmittance of a substantial percentage of light in the visible spectrum. A typical composite consists of a transparent substrate such as glass or flexible plastic film. Onto the substrate are deposited multiple stacks of discrete layers, each stack having in sequence a thin film of dielectric material and a heat reflecting metal such as silver, gold or copper.
Each of the layers is generally deposited by thermal evaporation deposition or by "sputtering" deposition, both techniques well-known in the art. For ease and economy of manufacture, each of the layers is typically deposited by sputtering deposition. In sputtering deposition methods, metal molecules from a source metal are induced to "sputter" onto a designated substrate by a strong electrical field under subatmospheric pressures. Where the layer deposited is to be pure metal, such sputtering is accomplished in an inert atmosphere. Where the layer is to be a metal oxide, such sputtering typically is carried out in a highly oxidative atmosphere using, for example, oxygen plasma.
A common problem with the manufacture of such composite structures is the degradation of the infrared reflecting metal layer by its exposure to oxygen plasma during the deposition of dielectric material (generally a metal oxide). Such degradation of the infrared reflecting metal significantly decreases the performance of the composite.
Another problem with such composite structures is the tendency of the infrared reflecting metals to degrade over long periods of time by long-term contact with oxygen or other chemicals from the surrounding atmosphere. This problem is especially acute where the structures are flexible film structures affixed to preexisting architectural or vehicular windows. The application of such films to such preexisting windows is typically carried out using water as described in U.S. Pat. No. 3,891,486, which is incorporated herein by this reference. In the application of such films to such preexisting windows, water used in the application tends to become trapped between the window glass and the flexible film. Over time, this trapped water diffuses through the flexible film to substantially degrade the reflecting metal layers within the composite structure.
Another problem with such composite structures is the general inability of such structures to successfully prevent the transmittance of excessive amounts of visible light. Transmittance of excessive visible light transmits unnecessary quantities of heat and can result in a displeasing "overly-bright" environment for the user.
Still another problem with such composite structures of the prior art is that they often reflect an inordinate percentage of visible light. Such high reflectances give the fenestration product an unpleasant mirror-like appearance. It is generally considered preferable for fenestration products to transmit less than about 15% of light within the visible spectrum.
Still another problem with composite structures of the prior art is that they often do not transmit and/or reflect light on both sides of the fenestration product in "neutral colors." This is especially a problem in products adapted to provide reduced (&lt;60%) visible light transmittance. Although it is considered acceptable for some fenestration products to transmit light which has a slightly blue or slightly green cast, all other "tints" are generally considered undesirable.
Attempts have been made to solve these problems, but such attempts have not been wholly successfully. For example, the disposition of a protective metal layer onto the infrared reflecting metal layer has been found to improve the degradation resistence of the infrared reflecting metal layer during the disposition of the dielectric layers. However, the use of such protective metal layer has not solved--and in many cases made more complicated--the problems of undue light transmittance, undue light reflectance and undesirable tint. Such attempts have also been commonly found to be unduly expensive in manufacture and/or unstable over long periods of time.
Accordingly, there is a need for a heat reflecting fenestration composite which effectively prevents the degradation of the infrared reflecting metal and which reduces the amount of transmitted visible light without causing excessive reflectance, color, distortion or long-term instability.